I have received rent due for the past period in the current financial year. How do I offer it to tax?

I have received rent due for the past period in the current financial year. How do I offer it to tax?

If you recover any rent that was not previously realized, then such unrealized rent shall be taxed in the year in which such income is realized by you (whether or not you are the owner of that property in that year) after deducting a sum equal to 30% of such unrealized rent.